(57) A capillary stop-flow junction located in a housing at an end of a capillary passageway used to transport a liquid and at the beginning of a non-capillary internal chamber in the housing, in which the stop-flow junction contains an improvement which comprises 1) means for selectively trapping a gas in the capillary passageway and non-capillary chamber, wherein when the means for trapping is activated and the liquid enters the capillary passageway, the gas is compressed by the liquid as the liquid flows through the capillary channel and stops flowing at the stop-flow junction ; or 2) a stop-flow nozzle surrounding the capillary passageway and projecting into the chamber ; or 3) the stop-flow junction being formed from a single housing body member ; or 4) a rupture junction in the capillary pathway, wherein the rupture junction is a stop-flow junction providing less maximum available back pressure than the capillary stop-flow junction. Diluters capable of serial dilution that use the stop-flow junctions of the invention are also described.